The present invention relates to a method and device for detecting partial discharge, in particular, a method and device for detecting partial discharge in a gas insulated device.
Conventional insulating devices include gas insulating switches, gas insulating buses, gas insulating transformers and oil transformers, which are all used in an electric power substation. These insulating devices insulate a high-voltage center conductor using an insulator, such as SF6, inside a sealed metal container or bushing. A defect such as a loose connection in the bushing or the existence of a foreign material in the bushing, can cause a dielectric breakdown of the electrical power device (substation).
A dielectric breakdown accident, which is one of the most serious accidents of an electrical power device, is often accompanied by a partial discharge as a forerunning phenomenon. Therefore, by detecting a partial discharge, an abnormality in the insulation of an electrical power device can be detected at an early stage or in an insignificant state in which a dielectric breakdown accident would not be caused. Thus, in an electrical power device, the preventive maintenance technique is important.
A conventional method for detecting a partial discharge provides an antenna (sensor) on a bushing lower tank of a bushing so that electromagnetic waves caused by partial discharge inside an insulating device can be detected. In other words, the antenna is typically provided in a base portion of the bushing. A cable typically connects to the antenna and is further connected to a conventional measuring device for measuring the discharge. Unfortunately, the conventional methods and devices for detecting a partial discharge provides low sensitivity to electromagnetic waves inside an insulating device due to interference from various component parts residing in the insulating device. Thus, a partial discharge cannot be timely or accurately detected in conventional methods and devices.
The present invention provides a method and device for detecting a partial discharge inside an insulating device with high sensitivity and accuracy.
In an object of the present invention a method for detecting a discharge in an electrical device is provided. The method comprises the acts of providing a bushing having a bottom lower flange and a top upper flange. Further the method provides a shield inside the bushing extending from the bottom lower flange to a position at least below the top upper flange and providing an antenna outside the bushing at least above the referenced position for measuring an output signal from the device for detecting the discharge.
In another object of the present invention a method for detecting a discharge in an electrical device is provided. The method comprises providing a bushing having a bottom lower flange and a top upper flange and providing an antenna outside the bushing at a position for measuring an output signal from the device for detecting the discharge. The method further provides the position be located above the bottom lower flange at about 3-20% of the distance between the bottom lower flange and top upper flange.
In yet another object of the present invention a discharge detector for an electrical device is provided comprising a bushing having a bottom lower flange and a top upper flange and a shield inside the bushing extending from the bottom lower flange to a position at least below the top upper flange. The detector further includes an antenna located outside the bushing at least above the referenced position for measuring an output signal from the device for detecting the discharge.
In yet another object of the present invention a discharge detector for an electrical device is provided comprising a bushing having a bottom lower flange and a top upper flange and an antenna outside the bushing at a position for measuring an output signal from the device for detecting the discharge. The position is located above the bottom lower flange at about 3-20% of the distance between the bottom lower flange and top upper flange.